The present invention is directed to wet processing methods for the manufacture of electronic components and electronic component precursors, such as semiconductor wafers used in integrated circuits. More specifically, this invention relates to methods of, for example, cleaning, stripping, and etching of electronic component precursors using dry displacement technology in conjunction with wet chemical processing techniques.
Wet processing is used extensively during the manufacture of integrated circuits, which typically comprise electronic component precursors such as semiconductor wafers, flat panels, and other electronic component precursors. Generally, the electronic component precursors are placed in a bath or a vessel and then contacted with a series of reactive chemical process fluids and rinsing fluids. The process fluids may be used, without limitation, for etching, photoresist stripping, and prediffusion cleaning and other cleaning steps of the electronic component precursors. See, e.g., U.S. Pat. Nos. 4,577,650; 4,740,249; 4,738,272; 4,856,544; 4,633,893; 4,775,532; 4,917,123; and EPO 0,233,184, assigned to a common assignee, and Burkman et al., Wet Chemical Processes-Aqueous Cleaning Processes, pg 111-151 in Handbook of Semiconductor Wafer Cleaning Technology (edited by Werner Kern, Published by Noyes Publication Parkridge, N.J. 1993), the disclosures of which are herein incorporated by reference in their entirety.
In a typical wet processing technique, electronic component precursors are exposed to reactive chemical process fluids to either remove (i.e., cleaning) contamination on the electronic component precursors or to etch some part of the surface. After this cleaning or etching is performed, the chemical will adhere to the surface or surfaces of the electronic component precursors. The adhered chemical must then be removed before treating the electronic component precursors with the next reactive chemical process fluid so that the chemical residue does not contaminate the next reactive chemical process.
Therefore, in current wet processing techniques, after each chemical treatment step, the electronic component precursors are rinsed with DI water to remove the chemicals from the surface or surfaces of the electronic component precursors, whether the chemical treatment is done in a bath, full flow vessel, or using other wet bench techniques. Sometimes a trace chemical may be added to the rinse water to give the rinsing fluid a certain property that may be beneficial. Even if the rinsing fluid (i.e., water) is modified with a trace chemical, its function is not changed. There is a clear distinction between chemicals that are used to perform, for example, the cleaning or etching action of the electronic component precursors and the rinsing fluid, which is intended to remove the chemicals from the surfaces of the electronic component precursors (even though the water may not be pure water but may have certain chemicals added to it).
In conventional techniques, a rinse with deionized (DI) water is always performed after the last chemical treatment step and before the wafers are dried, whether the chemical treatment is done in a bath, full flow vessel, or using other wet bench techniques. Although a DI rinse removes the given chemical from the surface of the electronic component precursors after the chemical has performed its function (e.g., cleaning or etching), this rinsing step imposes several limitations on the manufacture of semiconductor components. For example, it is standard in the industry to rinse the electronic component precursors between chemical treatment steps with DI water until the level of dissolved chemicals is about 10 p.p.b. (i.e., 4-16 Mohm-cm). This requires extensive rinsing.
Because DI water tends to be very expensive, rinsing substantially increases the costs of manufacturing electronic component precursors. DI rinsing also takes a long time, sometimes consuming as much as 60% of the total wet processing time, therefore decreasing throughput of the electronic component precursors.
The rinse with DI water can also compromise the integrity of the wet processing techniques by causing precipitation of residual material or by causing the formation of undesirable oxide, silica, and/or metal precipitates. A rinsing fluid, even when it is pure DI water is sometimes reactive with semiconductor materials such as silicon and can oxidize some silicon atoms on the surface of the semiconductor material.
In addition to rinsing electronic component precursors after treatment with reactive chemical process fluids, the electronic component precursors normally need to be dried. This can be a particularly challenging process because it is important that no contamination be created during the drying process. Evaporation is undesirable since it often leads to spotting or streaking. Even the evaporation of ultra high purity water can lead to problems because such water is very aggressive to the water surface and will dissolve traces of silicon and silicon dioxide during even short periods of water contact. Subsequent evaporation will leave residues of the solute material on the wafer surface. Contamination and other causes of semiconductor failure are discussed, for example, in J. Schadel, xe2x80x9cDevice Failure Mechanisms In Integrated Circuits,xe2x80x9d Solid State Devices 1983 Conf. Ser. No. 69 (Institute of Physics, London 1984) 105-120.
Conventionally, semiconductors are dried through centrifugal force in a spin-rinser-drier. Because these devices rely on centrifugal force to xe2x80x9cthrowxe2x80x9d water off the wafer surfaces, their use results in several problems. First, there are mechanical stresses placed on the wafers which may result in wafer breakage, particularly with larger wafer sizes. Second, because there are many moving parts inside a spin-rinser-drier, contamination control becomes a difficult problem. Third, since the wafers conventionally travel at high velocity through dry nitrogen, static electric charges develop on the wafer surfaces. Since oppositely charged airborne particles are quickly drawn to the wafer surfaces when the spin-rinser-drier is opened, particular contamination results. Fourth, it is difficult to avoid evaporation of water from the surfaces of the wafers during the spin process with the attendant disadvantages discussed above.
More recently, methods and apparatus have been developed for steam or chemical drying of wafers, including the method and apparatus disclosed in U.S. Pat. No. 4,778,532. Chemical drying generally comprises two steps. First, the rinsing fluid, preferably water is driven off the wafers and replaced by a nonaqueous drying fluid. Second, the nonaqueous drying fluid is evaporated using a predried gas, preferably an inert gas such as nitrogen at a low flow velocity.
Another chemical drying process currently used in Japan consists of sequentially immersing the wafer carrying vessel in tanks of deionized water, followed by suspending the wafers above a tank of boiling isopropanol. The wafer-carrying vessel is then slowly withdrawn from the isopropanol vapor to pull the water droplets off the wafer surfaces.
One of the most important features for an effective wafer drying technology is that the wafers produced be ultraclean (i.e., with minimum particle contamination and minimum chemical residue).
Thus, there is the need in the art for a simple and efficient method that permits the safe chemical treatment of electronic component precursors, while at the same time eliminating the problems and costs associated with DI rinsing after chemical treatment steps and the problems associated with drying electronic component precursors using conventional techniques. The present invention addresses these as well as other needs.
The invention presents, inter alia, wet processing methods useful in the manufacture of electronic component precursors, such as semiconductor wafers and flat panels, used in integrated circuits. These novel methods can be used for the cleaning, stripping, and/or etching of electronic component precursors, such as semiconductor wafers.
In conventional wet processing techniques, a reactive chemical process fluid is removed from the surface or surfaces of a electronic component precursors with a rinsing fluid, such as DI water. It has been discovered that a reactive chemical process fluid can be displaced from the surface of a semiconductor wafer by using a drying fluid, such as isopropyl alcohol instead of a rinsing fluid, thereby eliminating the final DI rinse of electronic component precursors. It is also contemplated that a drying fluid may be used between chemical treatment steps thereby eliminating or minimizing the need for DI rinses between chemical treatment steps. By eliminating the final DI rinse and minimizing the use of DI water between chemical treatment steps, the problems that may be associated with its use, such as precipitation of silica, metal, and/or oxide precipitates, can be minimized, if not avoided.
It has also been discovered that the drying fluid serves the additional function of drying the electronic component precursors, thus, eliminating the need for an additional drying step as in conventional wet processing techniques.
In particular, the invention is directed to a method for the manufacture of electronic component precursors comprising: placing the electronic component precursors in a reaction chamber; contacting the surfaces of said electronic component precursors with at least one reactive chemical process fluid for a selected period of time; and exposing the electronic component precursors to a drying fluid for a selected period, after the electronic component precursors have been exposed to the final reactive chemical process fluid.
In one aspect of the invention, the electronic component precursors are maintained in a single reaction chamber during the entire chemical treatment process. In this aspect of the invention, the electronic component precursors are placed in a reaction chamber and the surfaces of the electronic component precursors are contacted with one or more reactive chemical process fluids for a selected period of time without removing the electronic component precursors from the reaction chamber. If more than one reactive chemical process fluid is to be used for treating the electronic component precursors, the process fluids may be introduced sequentially into the reaction chamber such that one process fluid directly displaces the previous process fluid from the surface or surfaces of the electronic component precursors, thereby eliminating the step of a DI rinse, or by draining the chamber of one reactive chemical process fluid before exposing the electronic component precursors to another reactive chemical process fluid. It is also contemplated that a DI rinse may be used between chemical treatment steps. The DI rinse may directly displace the reactive chemical from the surface or surfaces of the electronic component precursors or the chamber may be drained before the DI rinse is introduced into the chamber. It is also contemplated that a drying fluid may be used between chemical treatment steps in place of a DI rinse. In such instances, the drying fluid would be introduced into the reaction chamber such that it would directly displace the reactive chemical process fluid from the surface or surfaces of the electronic component precursors.
In another aspect of the invention, the electronic component precursors are moved from one reaction chamber to another, wherein each reaction chamber contains a different reactive chemical process fluid. According to this aspect of the invention, after treating the electronic component precursors with one reactive chemical process fluid, the electronic component precursors are immediately immersed into the next reactive chemical process fluid contained in another reaction chamber without rinsing the electronic component precursors with a rinsing fluid to remove the previous reactive chemical process fluid from the surfaces of the electronic component precursors. It is contemplated, however, that the electronic component precursors can be immersed in a chamber containing a rinsing fluid in between chemical treatment steps. It is further contemplated that the electronic component precursors can be immersed in a chamber containing a drying fluid in between chemical treatment steps.
Regardless of the reaction chamber used for treating the electronic component precursors, in a preferred embodiment, following exposure of the electronic component precursors to the last reactive chemical process fluid, a drying fluid is supplied to the reaction chamber such that the it displaces the last reactive chemical process fluid from the surface or surfaces of the electronic component precursors preferably at such a rate that substantially no liquid droplets are left on the surfaces after replacement of the reactive chemical process fluid with the drying fluid. It is also contemplated that the electronic component precursors may be exposed to a drying fluid between chemical treatment steps, thereby eliminating the step of a DI rinse between each chemical treatment step.
The use of a drying fluid in place of a DI rinse to remove reactive chemical process fluids from the surface or surfaces offers the advantages of higher output of electronic component precursors. By eliminating the DI rinse and a separate drying step at the end of the wet processing technique, the methods of the invention result in a significant costs savings because DI water is very expensive. These are great benefits to the semiconductor manufacturing industry. The method of the invention offers improved safety because the reactive chemicals such as HF are removed from the ends of electronic component precursors, and prevents operators from being exposed to such hazardous chemicals. These methods also result in improved process performance of electronic component precursors (i.e., wafers or panels are cleaner).